To create or edit a surface concentration flux:

1. Display the surface concentration flux load editor using one of the following methods:

   • To create a new surface concentration flux load, follow the procedure outlined in “Creating loads,” Section 16.8.1 (Category: Mass diffusion; Types for Selected Step: Surface concentration flux).

   • To edit an existing surface concentration flux load using menus or managers, see “Editing step-dependent objects,” Section 3.4.13. To edit the region to which the load is applied, see “Editing the region to which a prescribed condition is applied,” Section 16.8.4.

2. Click the arrow to the right of the Distribution field, and select the option of your choice from the list that appears:

   • Select Uniform to define a load that is uniform over the surface.

   • Select User-defined to define the magnitude of the load in user subroutine DFLUX. See the following sections for more information:

     • “Specifying general job settings,” Section 19.8.6

     • “DFLUX,” Section 1.1.3 of the Abaqus User Subroutines Reference Guide

   • Select an analytical field, labeled with an (A), or a discrete field, labeled with a (D), to define a spatially varying load. Only analytical fields and discrete fields that are valid for this load type are displayed in the selection list.

     Alternatively, you can click to create a new analytical field. (See Chapter 58, “The Analytical Field toolset,” for more information.)

3. If you selected the Uniform, analytical field, or discrete field distribution option, perform the following steps:

   1. In the Magnitude text field, enter the concentration flux density (units PLT^–1). A positive magnitude indicates concentration flow into the surface.

   2. If desired, click the arrow to the right of the Amplitude field, and select the amplitude of your choice from the list that appears. Alternatively, you can click to create a new amplitude. (See Chapter 57, “The Amplitude toolset,” for more information.)

   3. Click OK to save your data and to exit the editor.

4. If you selected the User-defined distribution option, perform the following steps:

   1. If desired, enter the concentration flux density in the Magnitude field (units PLT^–1). A positive magnitude indicates concentration flow into the surface.

      Magnitude data that you enter in the editor are passed into the user subroutine.

   2. Click OK to save your data and to exit the editor.

   3. Enter the Job module and display the job editor for the analysis job of interest. (For more information, see “Creating, editing, and manipulating jobs,” Section 19.7.)

   4. In the job editor, click the General tab, and specify the file containing the user subroutine that defines the load magnitude. For more information, see “Specifying general job settings,” Section 19.8.6.

      Note:  You can specify only one user subroutine file in the job editor; if your analysis involves more than one user subroutine, you must combine the user subroutines into one file and then specify that file.